Fracture resistant domed insert

ABSTRACT

A cutting element for earth-boring drill bits comprising a generally domed cutting surface comprising a superabrasive material, formed by a high-pressure high-temperature sintering method known in the art, integrally bonded to a cylindrical substrate having a truncated conical interfacial surface, consisting of a top surface and a circumferential shoulder joined by tapered sidewalls, and the base of the substrate being adapted for insertion into an earth-boring tool. The top surface of the substrate may form a circle, a square, or a polygon, and the sidewalls may be smooth or form one or more polygons.

RELATED APPLICATIONS

[0001] None.

BACKGROUND OF THE INVENTION

[0002] This invention relates to cutting inserts for use in drillingsubterranean formations such as oil, gas, and geothermal wells. Moreparticularly, this invention relates to a cutting insert that iscomprised of a tough, hard metal substrate featuring a truncated conicalinterfacial surface. The cutting insert has one or more layers of asuperabrasive material are bonded under high-pressure andhigh-temperature to the interfacial surface in such a manner so as toform a generally domed cutting table. Inserts of the present inventiondemonstrate fracture toughness capable of withstanding the dynamic loadsassociated with drilling a variety of subterranean formations.

[0003] Cutting elements coated with superabrasive materials such aspolycrystalline diamond or cubic boron nitride are used widely in thedrilling industry for drilling deep oil, gas, and geothermal wells.Superabrasive cutting elements have been used on most styles of drillbits that are used for subterranean drilling. The roller cone bit is anexample of a drill bit that has benefited from the presence of at leastsome superabrasive cutting elements primarily located in the gage andheel rows of the bit. A roller cone bit usually has two or three conesthat are rotationally affixed to the bit body by means of sealedbearings. As the bit body is rotated under the load of the drill string,the individual cones rotate independently of each other. The cuttingelements arrayed about the cone bodies inflict a compressive stress onthe formation being drilled causing it to fail. The crushed rock isflushed away from the bit and carried to the surface by the circulatingdrilling fluid, or mud, and new rock is exposed to the cutting elementsof the bit.

[0004] Because superabrasive materials have high compressive strengths,they are an ideal material for use in deep well drilling. However, suchmaterials are susceptible to stress fractures that result in spalling,fracturing, and delamination of the superabrasive cutting table. Stresson the cutting table of the insert comes from both within the insert andfrom the formation being drilled. Stresses on the drill bit due tosubterranean conditions are largely controlled by the driller, butbecause of the differences in rates of thermal expansion, elasticmoduli, and bulk compressibilities between the superabrasive and thesubstrate to which it is bonded, enormous internal residual stresses arepresent along the interfacial surfaces of the cutting element. Thesestresses may lead to failure of the superabrasive coating despite theskill of the operator.

[0005] Studies have shown that by modifying the shape of the surface towhich the superabrasive is bonded residual stresses may be reduced andfracture toughness thereby increased. This patent discloses a domedcutting insert having a modified interfacial surface that yields asuperabrasive coating having sufficient fracture toughness to withstandthe compressive stresses of subterranean drilling.

SUMMARY OF THE INVENTION

[0006] The cutting element substrate of the present invention iscomprised of tough cemented metal carbides and has a cylindrical baseadapted for insertion into an earth-boring tool such as a roller conebits. The substrate of the cutting element of the present invention hasa truncated conical interfacial surface opposite its base end. Thetruncated conical interfacial surface is integrally bonded to asuperabrasive material such as polycrystalline diamond or cubic boronnitride at high pressure and high temperature. The actual shape of thetruncated conical surface may be round, oval, or a predeterminedpolygonal shape. The tapered sides of the truncated conical surface mayalso comprise flats having a predetermined polygonal shape such astrapezoid or rectangle. Additionally, the tapered sides of the conicalsurface may comprise flutes. The truncated conical surface may even havesurface protrusions or posts to further reinforce the superabrasivematerial to which it is bonded. Another variation includes a peripherallip on the edge of the truncated conical surface, which also increasesbonding strength. A circumferential shoulder is formed as the truncatedconical surface begins tapering from the base of the cylindricalsubstrate. The use of a truncated conical interfacial surface underlyingthe superabrasive generally domed cutting table permits the use of atough metal carbide substrate and decreases point pressure duringdrilling. Instead of high-pressure strains localized over a small areaduring drilling, the compressive and shear type stresses induced fromdrilling is spread out over the flat truncated conical surface therebyreducing overall strain on the cutting insert.

[0007] Superabrasive material used as a cutting surface is well known inprior art. The superabrasive material used in this invention consists ofnatural diamond, polycrystalline diamond, cubic boron nitrides, or anycombinations thereof The generally domed shape of the superabrasivematerial that forms the cutting table of the insert behaves much like acontinuous truss bridge with self-supporting arches and aninterconnected rigid framework. The self-supporting truss like strengthof the polycrystalline dome increases the overall fracture strength ofthe polycrystalline cutting surface. Working in concert with thegenerally domed cutting table, which may comprise polygonal surfaces,the truncated conical shape of the tough substrate reduces spalling,cracking, fracture, and delamination of the cutting surface duringcompressive drilling through a variety of subterranean formation,including those having periodic discontinuities such as hard rockstringers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a perspective view of a substrate depicting a truncatedconical interfacial surface with a supporting circumferential shoulder.

[0009]FIG. 2 is an aerial view of the substrate in FIG. 1.

[0010]FIG. 3 is cross sectional side view of one half of the substrateas taken through line 1-1 of FIG. 2.

[0011]FIG. 4 is an external side view of a cutting insert of the presentinvention depicting a generally domed cutting table.

[0012]FIG. 5 is a cross sectional side view of one half of the cuttingelement in FIG. 4 as taken through line 1-1 of FIG. 2 and including theintegrally bonded superabrasive cutting surface.

[0013]FIG. 6 is a perspective view of a substrate depicting a truncatedconical interfacial surface with a supporting circumferential shoulderand tapered rectangular flats.

[0014]FIG. 7 is an aerial view of the substrate in FIG. 6.

[0015]FIG. 8 is a cross sectional side view of one half of the substrateincluding the integrally bonded superabrasive cutting surface as takenthrough line 2-2 of FIG. 7.

[0016]FIG. 9 is an aerial view of a substrate depicting a truncatedconical interfacial surface with a square top surface, trapezoidal sideflats, and a supporting circumferential shoulder.

[0017]FIG. 10 is an aerial view of a substrate depicting a truncatedconical interfacial surface with an octagonal top surface, generallyrectangular side flats, and a supporting circumferential shoulder.

[0018]FIG. 11 is frontal cross-section view of a cutting insert of thepresent invention depicting polygonal surfaces of the cutting table.

[0019]FIG. 12 is a side cross-section view of the cutting insert of FIG.11 depicting polygonal surfaces of the cutting table.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Cutting elements associated with the present invention used inearth-boring tools typically consist of two main parts: a substrate madeof fracture tough material and a cutting surface, or cutting table,composed of a superabrasive material such as polycrystalline diamond orcubic boron nitride. The present invention relates to the shape of thecutting element substrate and the shape of the cutting surface, and howthose shapes combine to permit the use of a tough carbide substrate andto reduce point stress concentrations during compressive use. A detaileddescription and associated drawings are described below.

[0021] A substrate 12 composed of a fracture tough material isillustrated in FIG. 1, as an embodiment of the present invention. Thesubstrate 12 may consist of any number of fracture tough materials suchas tungsten carbide, nickel, cobalt, nickel or cobalt carbides, or anynumber of cemented carbide materials. The substrate 12 includes agenerally cylindrical base 11 for insertion into an earth-boring tool,such as a drill bit. A truncated conical interfacial surface 14 isformed at the opposite end of the substrate for supporting asuperabrasive cutting table. Truncated conical interfacial surface 14includes tapered sides 24 and a truncated top surface 26. The presentinvention includes variations in the shape of the truncated top surface26 and the tapered sides 24 which will be illustrated in later drawings.A supporting circumferential shoulder 22 is formed between the outerperimeter of the substrate 12 and the inner base perimeter of thetapered sides 24 of truncated conical interfacial surface 14. Thiscircumferential shoulder 22 connects the truncated conical interfacialsurface 14 with the cylindrical base 11. The circumferential shoulder 22may join the tapered side 24 at an obtuse angle, or it may be formedsubstantially perpendicular to the tapered sides 24 and generallyparallel to the truncated top surface 26. However, the shoulder formeddoes not need to be strictly perpendicular as will be noted in laterdrawings of the invention. The circumferential shoulder aids compactionof the superabrasive matrix during pre-sintering assembly and lendssupport to the superabrasive cutting surface during formation of thecutting element during the high pressure, high temperature process. Thesupporting circumferential shoulder 22 gives a sort of base layer uponwhich the superabrasive matrix can obtain its footing and buttressupward formation of the cutting surface. The truncated top surface 26and tapered sides 24 are substantially flat and smooth. The perimeter oftruncated top surface 26 may be defined by predetermined polygonalshapes, as illustrated in the drawings of this disclosure.

[0022]FIG. 2 is an aerial view of the substrate in FIG. 1. A circle 36defines the truncated conical surface perimeter of truncated top surface26. The tapered sides 24 slope upward and are cropped at a desiredheight forming truncated top surface 26. The circumferential shoulder 22is formed from the substrate body 12 and is of sufficient width tosupport the superabrasive before and during the sintering process of thedomed superabrasive cutting surface. The shoulder also gives support tothe cutting table during subterranean drilling, increasing the fracturetoughness of the cutting table.

[0023]FIG. 3 illustrates a cross sectional side view of the substratetaken along the lines 1-1 in FIG. 2. FIG. 3 includes only one half ofthe substrate, the other half being a mirror image of the illustratedhalf. The cylindrical base 11 of substrate 12 is adapted for insertioninto an earth-boring tool as shown by the chamfers on the edges. Thetruncated conical interfacial surface 14 includes truncated top surface26 and tapered sides 24. The transition from the tapered sides 24 to thetruncated top surface 26 may be gradual or abrupt. FIG. 3 depicts agradual transition from the circumferential shoulder 22 to the taperedsides 24 to the truncated top surface 26 while maintaining a definiteslope upward from the base to the plateau of the truncated conicalinterfacial surface 14. A gradual transition is preferred because of itseffect on the stresses along the junction of the shoulder and thetapered walls. The circumferential shoulder 22 in FIG. 3 issubstantially perpendicular to the tapered sides 24. This illustrationshows a filleted edge between the circumferential shoulder 22 and thetapered sides 24. Still, the edges between the two surfaces could beexactly perpendicular if desired and such a configuration is not outsidethe scope of the invention. Gentle sloping is however, the preferredvariation.

[0024]FIG. 4 illustrates an embodiment of the invention that combinesthe substrate with the generally domed cutting table. Cutting element 10comprises a fracture tough substrate 12 and a superabrasive cuttingsurface. The superabrasive material employed in the cutting surface iswell known in the prior art and common in the drilling industry. Thesuperabrasive material is selected from the group consisting of diamond,polycrystalline diamond, or cubic boron nitride. These materials areintegrally bonded to the substrate 12 during a high pressure, hightemperature sintering process. The terms PCD, polycrystalline diamond,diamond powder matrix, or superabrasive material will be used hereafterto refer to such materials. The superabrasive cutting surface 20 has agenerally domed shape 27 formed over the truncated conical interfacialsurface 14. The domed shape of the cutting surface combines with theinterfacial surface of the substrate to give the insert fracturetoughness suitable for drilling a variety of subterranean formations,including those where hard rock stringers are encountered.

[0025]FIG. 5 is a cross sectional side view of FIG. 4 taken throughlines 1-1 of FIG. 2. The cutting element 10, as shown in FIG. 5, is onehalf the cutting element in FIG. 4. Cutting element 10 includes agenerally cylindrical substrate 12 composed of fracture tough materialwith a base 11 adapted for insertion into an earth-boring tool. Oppositethe base end 11 of substrate 12 is a truncated conical interfacialsurface 14 consisting of a truncated top surface 26 and tapered sides24. Joining the truncated conical interfacial surface 14 to thesubstrate 12 is a circumferential shoulder 22 used to support thesuperabrasive cutting surface 20, especially during its formation. Asuperabrasive cutting surface 20 is formed on top of the truncatedconical interfacial surface 14. The superabrasive cutting surface 20 isintegrally bonded to the truncated conical interfacial surface 14 of thesubstrate through the high-pressure, high-temperature process. Thesubstrate 12 is placed into a generally domed loading container withdiamond powders and refractory metals creating a diamond matrix that isplaced over the substrate. When subjected to a high pressure, hightemperature process, the diamond powders contacting the truncated topsurface 26 and tapered sides 24 of the substrate 11 are pressed to forma superabrasive cutting surface 20 that takes on the shape of theloading container. The generally dome like shape 27 of superabrasivematerial bonded to the substrate yields superior compressive strength.Because of the thickness 25 of the cutting surface 20, the superabrasivedome 27 permits the use of a fracture tough carbide insert and acts likea self-supporting bridge or a continuous truss bridge. Theself-supporting truss like strength of the superabrasive dome 27increases overall fracture strength of the cutting surface 20 and thusincreases the lifetime of the cutting element 10.

[0026]FIG. 6 illustrates alternative embodiment of the presentinvention. The substrate 12 includes a cylindrical base 11 and truncatedconical interfacial surface 14. Unlike the cutting element in FIG. 1,the tapered sides 24 of the truncated conical interfacial surface 14 ofFIG. 6 are rectangular flats 34. The use of flat surfaces on the taperedsides of the substrate increases the volume of superabrasive materialused in the cutting element. The higher volume of superabrasive materialin the cutting table increases the life of the cutting surface while thegenerally domed configuration of the cutting table in combination withthe truncated conical interfacial surface provides a cutting elementhaving sufficient fracture toughness to withstand the dynamic loadsassociated with oil and gas well drilling. A circle 36 defines the topsurface perimeter of the truncated top surface 26. A shoulder 22 isformed substantially perpendicular to the tapered sides 24 of truncatedconical interfacial surface 14. This drawing shows how the shoulder neednot be strictly perpendicular to the tapered sidewalls of the truncatedconical interfacial surface but is generally parallel to the truncatedtop surface 26. The shoulder 18 lends support to the superabrasivecutting surface during formation of the cutting element through a highpressure, high temperature process. The shoulder 22 gives a sort of baselayer upon which the diamond powder matrix can obtain its feet. Thistype of shape behaves much like a continuous truss bridge withself-supporting arches and an interconnected rigid framework. Theself-supporting truss-like strength of the polycrystalline domeincreases the overall fracture strength of the polycrystalline cuttingsurface. The generally domed cutting table, in concert with thetruncated conical interfacial surface of the substrate of the presentinvention, enables the cutting element to withstand spalling, cracking,fracture, and delamination of the cutting surface during compressivedrilling.

[0027]FIG. 7 illustrates a top view of substrate 12 in FIG. 6 withtruncated top 26 in circular shape 36. Forming the tapered sides 24leading up to the truncated top 26 are rectangular flats 34. Asupporting circumferential shoulder 22 forms the outer top perimeter ofthe substrate 12.

[0028]FIG. 8 depicts a cross sectional side view of FIG. 7 as takenthrough lines 2-2 of FIG. 7. A cutting element 10 as shown in FIG. 8 isone half of the element in FIG. 7. Cutting element 10 includes agenerally cylindrical substrate 12 with base end 11 adapted forinsertion into an earth-boring tool. Opposite the base end 11 is atruncated conical interfacial surface 14, which includes truncated topsurface 26 and tapered sides 24. Connecting the truncated conicalinterfacial surface with the substrate is a circumferential shoulder 22.In this particular embodiment of the invention, it is noted how theformation of the truncated top surface, tapered sides, andcircumferential shoulder differ from the previous embodiment. Thisembodiment employs a series of oblique angles to define the junctionbetween the truncated top surface to the tapered sides and the taperedsides to the circumferential shoulder. Thus the transitions from thetruncated top to the tapered sides and from the tapered sides to thecircumferential shoulder are not substantially perpendicular. Theseoblique transitions serve to relieve points of stress concentration thatmight otherwise be present. Additionally, the corners forming theintersection of the oblique angles are not filleted but abrupt andclearly defined as opposed to the substrate in FIG. 3. The truncatedconical interfacial surface 14 is specifically fashioned to bond withthe cutting surface 20 during a high pressure, high temperaturesintering process. The cutting surface 20 is formed to have a generallydome like shape 27 with a substantial thickness 25 on top of thetruncated conical interfacial surface 14. This type of shape behavesmuch like a continuous truss bridge with self-supporting arches and aninterconnected rigid framework. The self-supporting truss like strengthof the polycrystalline dome increases the overall fracture strength ofthe polycrystalline cutting surface.

[0029]FIGS. 9 and 10 illustrate other variations in the shape of thetruncated conical interfacial surface of the substrate. However, thecross sectional side view as depicted in FIG. 8 is not different forboth substrates depicted in FIGS. 9 and 10 as well as the general shapethe base portion of the substrate. In fact, FIG. 8 depicts a crosssectional side view taken along lines 3-3 and 4-4 of FIGS. 9 and 10respectively. Accordingly, only aerial views of the various truncatedconical interfacial surfaces of FIGS. 9 and 10 are illustrated. FIG. 9depicts a truncated conical interfacial surface that is roughly theshape of a truncated pyramid. The truncated pyramid includes a truncatedtop surface 26 with a square perimeter 46 and tapered sides 24 formingtrapezoids 44. The tapered sides formed are not strictly limited todefinitional trapezoids as the base side of the trapezoids shown formsan arc whereas conventional trapezoids have two sides parallel to eachother. Either variety however can be formed depending on manufacturerinterests. Interconnecting the trapezoidal sides 44 and the outerperimeter of the substrate 12 is the circumferential shoulder 22. Asnoted earlier, the flat surfaces along the tapered walls of theinterfacial surface serve to increase the volume of superabrasivematerial present in the cutting element. The higher volume of materialnot only serves to increase fracture toughness of the cutting element,it also adds to the overall life of the cutting table.

[0030]FIG. 10 illustrates another variation in the shape of thetruncated top 26 of the truncated conical interfacial surface of thesubstrate 12. Truncated top 26 is an octagonal shape 56 formed bytapered sides 24 in the shape of rectangular flats 54. Again,interconnecting the trapezoidal sides 54 and the outer perimeter of thesubstrate 12 is the circumferential shoulder 22. Interconnecting thetrapezoidal sides 44 and the outer perimeter of the substrate 12 is thecircumferential shoulder 22. Various shapes in the truncated conicalinterfacial surface yield different surface areas, which affect thebonding strength between the substrate and the superabrasive cuttingsurface.

[0031]FIG. 11 illustrates a face-on cross-sectional view of yet anotherversion of the present invention wherein the cutting insert 10 comprisesa tough carbide base portion 12 and a cutting table 27 comprising asuperabrasive material 20 that is bonded to the substrate in a highpressure high temperature sintering process. FIG. 12 is a side view ofthe insert of FIG. 11. The substrate 12 presents a cylindrical shapewhile the interfacial surfaces, consisting of the shoulder 22, thetapered sides 24, and top surface 26, form a polygonal interfacialsurface, such as an oval, to which the superabrasive is bonded. Thebroad face of the cutting table serves to increase the area ofpenetration of the cutting insert and the increased surface area of thecutting table reduces point stress concentration. The increased depth ofthe superabrasive permits the use of a tough carbide substrate whileimparting truss-like strength to the cutting table. These elementscombine to produce a cutting insert suitable for penetrating fractureresistant subterranean formations.

[0032]FIG. 13 illustrates a cross sectional view of another version of acutting insert 10 of the present invention wherein the cutting table 27is a truncated cone mounted onto a cylindrical substrate 12. As in theformer versions of the present invention, the top of the substrate 20may present a plane circle or a polygon. The relatively sharp truncatedconical cutting table 27 may be particularly useful in soft formationswhere an aggressive cutting insert is acceptable.

[0033] Other possible variations of the invention not shown in thedrawings, but known in the art, are presented here. One variation may beto provide tapered sides having reinforcing nodules extending into thecutting surface. The purpose of such posts is to further reinforce andstrengthen the cutting surface, to promote adhesion of the cutting tableto the substrate, and to prevent substantial cracking, spalling, anddelamination during compressive drilling.

[0034] Another variation to the truncated conical interfacial surface istapered sides having flutes. The flutes increase the surface area of thetruncated conical interfacial surface and enhance adhesion strength ofthe cutting surface to the substrate.

[0035] One advantage of the present invention is its unidirectionalbehavior meaning that the cutting insert can rotate in any direction andstill perform productively. Some cutting inserts in the prior art aredirectionally based and must be correctly implanted in the rotatingdrill head to function properly. If a mistake is made in the setting ofsuch cutting elements in the rotating drill head, boring efficiency isreduced and cutting element failure imminent. With the presentinvention, no such problems exist. The insert can be placed into therotating drill bit with ease and without undue concern for itsorientation.

What is claimed:
 1. A cutting element for earth-boring drill bits,comprising: a generally domed cutting surface comprising a superabrasivematerial, formed by a high-pressure high-temperature sintering methodknown in the art, integrally bonded to a cylindrical substrate having agenerally truncated conical interfacial surface, consisting of a topsurface and a circumferential shoulder joined by tapered side walls, andthe base of the substrate being adapted for insertion into anearth-boring tool.
 2. The cutting element of claim 1, wherein thesurfaces of the generally domed cutting table comprise polygonal shapedsurfaces.
 3. The cutting element of claim 1, wherein the generally domedcutting table has sufficient thickness to withstand compressive drillingof subterranean formations.
 4. The cutting element of claim 1, whereinthe substrate is composed of a fracture tough material selected from thegroup consisting of cemented metal carbide.
 5. The cutting element ofclaim 1, wherein the truncated interfacial surface comprises a topsurface forming a circle, a square, a polygon, or a combination thereof.6. The cutting element of claim 1, wherein the tapered walls of theinterfacial are surface smooth.
 7. The cutting element of claim 1,wherein the tapered walls of the interfacial surface form one or morepolygons.
 8. The cutting element of claim 1, wherein the tapered wallsof the interfacial surface form a truncated pyramid.
 9. The cuttingelement of claim 1, wherein the tapered sidewalls join thecircumferential shoulder at an oblique angle.
 10. The cutting element ofclaim 1, wherein the tapered sidewalls join the shoulder and top along afilleted surface.